Atrial tachyarrhythmia detection system and method

ABSTRACT

A system and method provide for detecting atrial arrhythmias within an implantable medical device capable of sensing and pacing at least an atrium of a heart. Arrhythmia of the atrium is detected. In response to detecting atrial arrhythmia, delivery of pacing signals to the atrium is inhibited under certain conditions. While delivery of the pacing signals to the atrium is inhibited, the detected arrhythmia of the atrium is confirmed during a period of further evaluation. Delivery of pacing signals to the atrium is enabled upon ceasing of the atrial arrhythmia. Inhibiting delivery of the pacing signals during atrial arrhythmia evaluation advantageously provides for an increase in the rate at which the detected arrhythmia is confirmed.

RELATED PATENT DOCUMENTS

This is a divisional of U.S. patent application Ser. No. 09/827,763,filed on Apr. 6, 2001, to which Applicant claims priority under 35U.S.C. § 120, and which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesand, more particularly, to implantable pacemakers andcardioverter-defibrillators that detect and treat atrialtachyarrhythmias.

BACKGROUND OF THE INVENTION

Implantable cardioverter-defibrillators (ICDs) have been developed thatemploy detection algorithms capable of recognizing and treating atrialtachycardias and atrial fibrillation. In general, ICDs are designed totreat such tachycardias with antitachycardia pacing and low-energycardioversion shocks in conjunction with back-up defibrillation therapy.These ICDs monitor the heart rate and the onset of the arrhythmia bysensing endocardial signals and determining when the heart is in need ofeither cardioversion to treat a given tachycardia or of defibrillationto treat a fibrillation condition.

While the combination of antitachycardia pacing with low and high energyshock delivery, as well as backup bradycardia pacing, in ICDs hasexpanded the number of clinical situations in which the devices mayappropriately be employed, improved means of coordinating atrial rateinformation in a way that results in a system that effectively andefficiently treats atrial tachyarrhythmias is still desired.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading thepresent specification, there is a need in the art for improved atrialarrhythmia detection techniques. There exists a further need for suchtechniques that provide for an increase in the speed at which atrialarrhythmias are evaluated and confirmed. The present invention fulfillsthese and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to a system and method for detectingatrial arrhythmias. An atrial arrhythmia detection methodology of thepresent invention is implemented with an implantable medical devicecapable of sensing and pacing at least an atrium of the heart. Accordingto one embodiment, arrhythmia of the atrium is detected. In response todetecting arrhythmia of the atrium, delivery of pacing signals to theatrium is inhibited to prevent competitive pacing of the atrium. Whiledelivery of the pacing signals to the atrium is inhibited, the detectedarrhythmia of the atrium is confirmed during a period of furtherevaluation. Inhibiting delivery of the pacing signals during atrialarrhythmia evaluation advantageously provides for an increase in therate at which the detected arrhythmia is confirmed. Delivery of pacingsignals to the atrium is enabled after the detected atrial arrhythmiahas ceased.

According to an embodiment of the present invention, high atrialinterval rates indicative of atrial arrhythmia are detected. Delivery ofpacing signals to the atrium is inhibited in response to detecting thehigh atrial interval rates, such as in response to detecting atrialflutter or other atrial arrhythmias. For example, delivery of pacingsignals to the atrium is inhibited in response to detecting atrialinterval rates of between about 130 and 230 beats per minute (bpm). Thedetection threshold for inhibiting atrial pacing is programmable,typically between 130 and 230 bpm, with 170 bpm representing a nominalthreshold.

Atrial intervals are detected while delivery of the pacing signals tothe atrium is inhibited. Atrial intervals are classified in an atrialwindow. The atrial window has a length and an associated firstsatisfaction criterion. An atrial episode is declared in response tosatisfying the atrial window by comparing classified atrial intervals tothe first satisfaction criterion. Inhibiting delivery of the pacingsignals during detection of high atrial interval rates advantageouslyprovides for an increase in a rate of atrial window satisfaction.

In one approach, delivery of atrial paces is inhibited during adetection window initiated in response to detecting high atrial intervalrates indicative of atrial arrhythmia. By way of example, an atrialevent occurring within a post-ventricular atrial refractory period(PVARP) is detected. A detection window is initiated in response to thedetected atrial event. Delivery of an atrial pace signal is inhibitedduring the duration of the detection window. A subsequent atrial eventmay be detected before expiration of the detection window. In this case,a subsequent detection window is initiated in response to the detectedsubsequent atrial event. Delivery of a subsequent atrial pace signal isinhibited during the subsequent detection window.

The atrial window may have a length that ranges between 20 and 60 atrialinterval samples. The first satisfaction criterion represents apredetermined number, percentage or ratio of the atrial intervalsclassified as fast atrial intervals relative to the atrial windowlength. For example, the first satisfaction criterion may representabout 80 percent of the atrial intervals classified as fast atrialintervals.

Further processes may involve verifying that the declared atrial episodeis a sustained atrial episode in response to the atrial window beingsatisfied by a second satisfaction criterion for subsequent atrialintervals. Each of the first and second satisfaction criterionrepresents a predetermined number, percentage or ratio of the atrialintervals classified as fast atrial intervals relative to the atrialwindow length, and the second satisfaction criterion is less than thefirst satisfaction criterion. By way of example, the first satisfactioncriterion may represent about 80 percent of the atrial intervalsclassified as fast atrial intervals and the second satisfactioncriterion may represent about 60 percent of the subsequent atrialintervals classified as fast atrial intervals.

In accordance with another embodiment of the present invention, atrialevents occurring within a post-ventricular atrial refractory period(PVARP) are detected. One or more detection windows is initiated inresponse to the detected atrial events. Delivery of atrial pace signalsis inhibited during the duration of the respective detection windows.While inhibiting delivery of the atrial pace signals, atrial intervalsare classified in an atrial window having a length and an associatedsatisfaction criterion. An atrial episode is declared in response tosatisfying the atrial window by comparing classified atrial intervals tothe satisfaction criterion.

According to a further embodiment of the present invention, a bodyimplantable system includes at least one lead comprising an atrialelectrode for sensing and pacing an atrium of a heart. A detector,coupled to the lead, detects high atrial interval rates indicative ofatrial arrhythmia. Memory is configured to define an atrial windowhaving a first length and a first satisfaction criterion. A controlcircuit is coupled to the detector and memory. The control circuitinhibits delivery of pacing signals to the atrium in response todetecting the high atrial interval rates. The detector detects atrialintervals while inhibiting delivery of the pacing signals to the atrium.The control circuit classifies the atrial intervals in an atrial windowand declares an atrial episode in response to satisfying the atrialwindow by comparing classified atrial intervals to the firstsatisfaction criterion.

The control circuit inhibits delivery of the pacing signals during adetection window initiated in response to detecting high atrial intervalrates indicative of atrial arrhythmia. For example, the detector detectsan atrial event occurring within a post-ventricular atrial refractoryperiod (PVARP), and the control circuit initiates a detection window inresponse to the sensed atrial event and inhibits delivery of an atrialpace signal during the detection window. The detector further detects asubsequent atrial event occurring before expiration of the detectionwindow. In this case, the control circuit initiates a subsequentdetection window in response to the sensed subsequent atrial event andinhibits delivery of a subsequent atrial pace signal during thesubsequent detection window.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of an implantable medical device with which atrialarrhythmia detection methodologies of the present invention may bepracticed;

FIG. 2 is a block diagram of several components housed in theimplantable medical device of FIG. 1;

FIG. 3 is a flow chart depicting various processes of an atrialarrhythmia detection methodology in accordance with an embodiment of thepresent invention;

FIG. 4 is a flow chart depicting various processes of an atrialarrhythmia detection methodology in accordance with another embodimentof the present invention;

FIGS. 5A-5B are flow charts depicting various processes of an atrialarrhythmia detection methodology in accordance with yet anotherembodiment of the present invention;

FIG. 6 illustrates the delivery of an atrial pace during a detectedatrial arrhythmia which disadvantageously reduces the rate of atrialdetection decisions; and

FIG. 7 illustrates inhibiting of an atrial pace during a detected atrialarrhythmia which advantageously increases the rate of atrial detectiondecisions according to an embodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail hereinbelow. It is to beunderstood, however, that the intention is not to limit the invention tothe particular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings which form a part hereof, and inwhich is shown byway of illustration, various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

Referring now to the figures, and more particularly to FIG. 1, there isshown a body implantable system 20 that represents one of several typesof systems with which atrial arrhythmia detection methodologies of thepresent invention may be practiced. For example, the implantable pulsegenerator 22 may be representative of all or part of a pacemaker,defibrillator, cardioverter, cardiac monitor, or re-synchronizationdevice. Accordingly, the arrhythmia detection methodologies of thepresent invention may be practiced in a wide variety of implantablemedical devices that sense cardiac activity.

The body implantable system 20 is shown to include an implantable pulsegenerator 22 coupled to an atrial lead 24 and a ventricular lead 26. Thesystem 20 may also include endocardial pacing andcardioversion/defibrillation leads (not shown) that are advanced intothe coronary sinus and coronary veins to locate the distal electrode(s)adjacent to the left ventricle or the left atrium. The distal end ofsuch coronary sinus leads is advanced through the superior vena cava,the right atrium, the valve of the coronary sinus, the coronary sinus,and into a coronary vein communicating with the coronary sinus, such asthe great vein. Typically, coronary sinus leads do not employ anyfixation mechanism and instead rely on the close confinement withinthese vessels to maintain each electrode at a desired site.

It is understood that an atrial arrhythmia detection methodology of thepresent invention may be practiced without inclusion of the ventricularlead 24 and/or a coronary sinus lead, and in configurations in whichonly the atria are paced and sensed. It is further understood that anatrial arrhythmia detection approach consistent with the principles ofthe present invention may also be practiced in devices that provide fordual chamber pacing and sensing, such as that depicted in FIG. 1 anddescribed in greater detail hereinbelow.

The system 20, as shown in FIG. 1, is implanted in a human body 28 withportions of the atrial and ventricular leads 24 and 26 inserted into aheart 30 to detect and analyze electric cardiac signals produced by boththe atria 32 and the ventricles 34 of the heart 30. The atrial andventricular leads 24 and 26 also provide electrical energy to the heart30 under certain predetermined conditions to treat various types ofcardiac arrhythmia, including, for example, atrial and ventriculartachycardias, and atrial and ventricular fibrillation of the heart 30.

A block diagram of the implantable pulse generator 22 electronics isprovided in FIG. 2. The implantable pulse generator 22 includes ahousing 36 which contains, among other components, a controller 100 andmemory 102, which typically includes read only memory (ROM) and randomaccess memory (RAM). Pulse generator 22 further includes a detector 104,which includes atrial and ventricular sense amplifiers (not shown), atherapy delivery unit 106, and a telemetry unit 108. The electroniccomponents of the pulse generator 22 are interconnected by way of a busconnection (not shown).

Power to the implantable pulse generator 22 is supplied by anelectrochemical battery 114 which is contained within the implantablepulse generator housing 36. The implantable pulse generator 22 isinterrogated and programmed via bi-directional radio frequency telemetrythrough cooperative operation between the telemetry unit 108 and anexternal programmer in a manner known in the art.

The atrial arrhythmia detection methodologies implemented by system 20are embodied in one or more algorithms as firmware within memory 102,and are executed by the controller 100. The detector 104 is alsoconnected to the controller 100, and contains a plurality of electricalconnections 110 coupled to the atrial and ventricular sense amplifiers.The outputs of the sense amplifiers are connected to the controller 100,such that atrial and ventricular signals received through the detector104 are analyzed by the algorithms implemented within the controller100. The controller 100 is also coupled to the therapy delivery unit106, which controls the delivery of electrical energy to the heart 30through a plurality of electrical output connections 112 to affect thesinus rhythm of the heart 30 under certain combinations of atrial 32 andventricular 34 conditions.

Referring again to FIG. 1, a connector block 38 is mounted on theimplantable pulse generator 22. The connector block 38 has two connectorports for coupling the atrial lead 24 and the ventricular lead 26 to thedetector 104 and the therapy delivery unit 106 of the implantable pulsegenerator 22. Additional connector ports can be added to the connectorblock 38, as in the case of configurations having three or more ports asis known in the art. Alternatively, the connector block 38 can beprovided with one connector port for coupling an implantable transvenouslead to the implantable pulse generator 22. It is understood that atrialand ventricular sensing and pacing/defibrillating functions may beaccomplished using a single lead system employing atrial and ventricularconductors/electrodes, rather than by use of the dual lead system shownin FIG. 1.

It is understood that atrial and, if applicable, ventricular sensing andpacing/defibrillating functions may be accomplished using a single leadsystem employing atrial and, if desired, ventricularconductors/electrodes, rather than by use of the dual lead system shownin FIG. 1. In one embodiment, a single atrial lead may be used in orderto accomplish the sensing and pacing/defibrillating functions associatedwith an atrium of the heart.

In general, the electrical activity in the heart 30 is sensed, andtherapies are delivered to the heart 30, through at least onetransvenous pacing/defibrillation lead connected to the implantablepulse generator 22. Unipolar and/or bipolar pacing and sensingelectrodes can be used in conjunction with the transvenouspacing/defibrillation lead. In the embodiment shown in FIG. 1, bipolarleads and sensing circuits are utilized for sensing both the atrial 32and the ventricular 34 activity. Sensing atrial activity includes thedetermination of atrial P-waves for purposes of determining atrialintervals. Ventricular activity is monitored by sensing for theoccurrence of ventricular R-waves for purposes of determiningventricular intervals. Pacing therapies to the atrium 32 or ventricle 34are delivered to the heart 30 using these same leads.

The system 20 may also employ defibrillation electrodes which areconnected to the electrical output connections 112, and serve to delivercardioversion and defibrillation level electrical pulses to the heart 30as determined by the programming of controller 100. The housing 36 ofthe system 20 may be used as an optional defibrillation electrode, wherethe housing 36 of the implantable pulse generator 22 is electricallyconnected to a cathode pole of the therapy delivery unit 106. Alldefibrillation electrical pulses are delivered to the heart with atleast two defibrillation electrodes, or through at least onedefibrillation electrode and the housing 36 of the implantable pulsegenerator 22. The system 20 supports a number of pacing regimens.

In addition to the lead configuration shown in FIG. 1, the system 20supports several other atrial lead configurations and types. Forexample, it is possible to use atrial endocardial bipolar pace/sensing,epicardial patches, and ancillary leads in conjunction with theimplantable pulse generator 22.

In the embodiment of system 20 depicted in FIG. 1, the atrial lead 24has an elongate body 40 having a peripheral surface 42, proximal anddistal ends, 44 and 46, a first atrial electrode 48 and a second atrialelectrode 50 on the peripheral surface 42. The first atrial electrode 48and the second atrial electrode 50 receive bipolar electrical cardiacsignals from the right atrium chamber 52 of the heart 30, and areattached on the peripheral surface 42 of the elongate body 40.

The first atrial electrode 48 is situated at or adjacent to the distalend 46 of the elongate body 40 and is either a pacing tip electrode or asemi-annular or annular electrode partially or completely encircling theperipheral surface 42 of the elongate body 40. The second electrode 50is an annular or semi-annular electrode encircling or partiallyencircling the peripheral surface 42 of the elongate body 40. The secondelectrode 50 is spaced longitudinally along the peripheral surface 40from the first atrial electrode 48 and the distal end 46 of the atriallead 24, such that when the atrial lead 24 is inserted into the rightatrial chamber 52 of the heart 30, the first atrial electrode 48 is inphysical contact with a portion of a wall of the right atrial chamber 52of the heart 30 and the second electrode 50 is within the right atriumchamber 52.

Electrical conductors extend longitudinally within the elongate body 40of the atrial lead 24 from a connection end at the proximal end 44 andmake connection to the first and second atrial electrodes 48 and 50. Theproximal end 44 of the atrial pacing lead 24 is attached to theconnector block 38 of the implantable pulse generator 22. The connectorblock 38 provides electrical coupling between the contact ends of theelectrical conductors of atrial lead 24 with the atrial sense amplifierof the detector 104 and the therapy delivery unit 106, such that theimplantable pulse generator 22 receives bipolar signals from anddelivers bipolar pacing to the right atrium 52 of the heart 30.

The ventricular lead 26, if used in combination with the atrial lead 24,includes an elongate body 54 having a peripheral surface 56, proximaland distal ends, 58 and 60, and a ventricle pacing electrode 62. Theventricular lead 26 also includes a first defibrillation electrode 64and a second defibrillation electrode 66 situated on the peripheralsurface 56 of the elongate body 54. The ventricular pacing electrode 62and the first defibrillation electrode 64 are adapted to receiveelectrical cardiac signals from the right ventricle chamber 68 of theheart 30, and are attached on the peripheral surface of the elongatebody 54. The second defibrillation electrode 66 is spaced apart andlongitudinally on the peripheral surface 56 of the ventricular lead 26.This configuration affords positioning of the ventricular lead 26 in theheart 30 with the ventricular pacing electrode 62 in the apex of theright ventricle 68, the first defibrillation electrode 64 within theright ventricle chamber of the heart, and the second defibrillationelectrode 66 within the right atrium chamber 52 or a major vein leadingto right atrium.

Electrical leads extend longitudinally within the elongate body 54 ofthe ventricular lead 26 from a connection end at the proximal end 58 tomake connection with the ventricular pacing electrode 62, the firstdefibrillation electrode 64, and the second defibrillation electrode 66.The proximal end 58 of the ventricular lead 26 is attached to theconnector block 38 of the implantable pulse generator 22. The connectorblock 38 provides for electrical coupling between the contact ends ofthe electrical conductors of ventricular lead 26 with the ventricularsense amplifier of the detector 104 and the therapy delivery unit 106,such that the implantable pulse generator 22 receives either unipolar orbipolar signals from, and can deliver unipolar or bipolar pacing to, theright ventricle 68 and defibrillation electrical pulses to theventricles 34 of the heart 30.

The atrial lead 24 and, if applicable, the ventricular lead 26 arereleasably attached to, and are separated from, the implantable pulsegenerator 22 to facilitate insertion of the leads 24, 26 into the heart30. The proximal end 44 of the atrial lead 24 and the proximal end 58 ofthe ventricular lead 26 are adapted to seal together with the connectorports of the implantable pulse generator 22 to thereby engage thecontact ends of the atrial lead 24 and the ventricular lead 26 with theplurality of electrical connections 110 and the therapy delivery unit106 of the implantable pulse generator 22. The implantable pulsegenerator 22 of the system 20 is then positioned subcutaneously withinthe body 26.

Referring now to FIG. 3, there is shown a flow diagram that describesvarious processes involving an atrial arrhythmic detection methodologyin accordance with an embodiment of the present invention. Themethodology depicted in FIG. 3 may be implemented using IMD circuitrydescribed hereinabove.

Atrial arrhythmias are, in general terms, dysrhythmias of the atria,which may include a variety of atrial tachycardias, including atrialfibrillation, atrial flutter, inappropriate sinus tachycardia, andparoxysmal supraventricular tachycardias, for example. Because many ofthese atrial arrhythmias have potential long term consequences, such astachycardia-mediated cardiomyopathy, as well as the development ofchronic atrial fibrillation from other atrial tachyarrhythmias,appropriate detection and treatment is important.

It has been found by the inventors that conventional treatment therapiesthat involve atrial pacing to regulate atrial activity in response tocertain atrial arrhythmias may have the unintended effect of slowing theatrial arrhythmia detection and confirmation process. In particular, ithas been determined by the inventors that delivery of atrial pacingduring the atrial arrhythmia detection and confirmation process resultsin a reduction in the rate at which atrial arrhythmia detection can beaccomplished. An A-A interval that ends with an atrial pace isconsidered a “slow” atrial interval. Application of an atrial arrhythmiadetection scheme that processes such “slow” atrial intervalsdisadvantageously arrives at a detection decision at a reduced speed.

An atrial arrhythmia detection methodology of the present inventionadvantageously avoids processing of slow atrial intervals and, as aresult, arrives at a detection decision at an increased speed relativeto conventional detection techniques. An atrial arrhythmia detectionmethodology of the present invention provides for increased atrialarrhythmia detection and confirmation by inhibiting atrial pacing duringa time in which the atrial arrhythmias evaluated. Inhibiting atrialpacing during such period of evaluation advantageously prevents theoccurrence of slow atrial intervals.

FIGS. 6 and 7 respectively illustrate the effects of providing for (FIG.6), and inhibiting (FIG. 7), atrial paces during a detected atrialarrhythmia. FIG. 6 illustrates the delivery of an atrial pace during adetected atrial arrhythmia which disadvantageously reduces the rate ofatrial detection decisions. FIG. 7 illustrates inhibiting of an atrialpace during a detected atrial arrhythmia which advantageously increasesthe rate of atrial detection decisions according to an embodiment of thepresent invention.

With regard to FIG. 6, the fast atrial sense following the atrial paceis not detected, thereby precluding this fast atrial sense from beingcaptured and evaluated in an atrial window. It can be appreciated thatexcluding this and other fast atrial sense samples following atrialpaces as shown in FIG. 6 reduces the rate at which atrial detectionwindow decisions can be accomplished.

In accordance with the principles of the present invention, atrial pacesare inhibited during a transitional period in which atrial activity isdetected as progressing from a normal condition to an arrhythmiccondition. This transitional period may also be characterized as aperiod in which ventricular rhythm management is disassociated fromatrial activity (i.e., atrial tracking) as a result of detecting rapidfast atrial responses. Delivery of pacing signals to the atrium isinhibited upon detecting atrial arrhythmia during this transitionalperiod. Inhibiting atrial paces during this transitional periodadvantageously increases the rate at which a detected atrial arrhythmiais confirmed.

According to one embodiment, an atrial flutter response (AFR) mechanismof system 20 is provided to prevent pacing into the atrial vulnerableperiod and to provide immediate fallback for atrial rates higher than anAFR programmable rate. This fallback is maintained as long as atrialevents continually exceed the AFR programmable rate. The term fallbackis generally understood in the art as a programmed rate, in the contextof dual-chamber pacing/defibrillation devices, to which the ventricularpacing rate falls back when the upper atrial rate limit has beenexceeded due to atrial tachyarrhythmia. It is to be understood that theAFR mechanism described herein is applicable to any type of atrialarrhythmia, and that the AFR nomenclature is used for convenience only.

When, for example, AFR provided by the system 20 is programmed to 170bpm, a detected atrial event inside the PVARP or a previously triggeredAFR interval will start an AFR window of a given duration (e.g., 350ms). It is understood that the programmable AFR window duration may bevaried, such as between 260 ms and 460 ms, for example. FIG. 7 shows afirst AFR window initiated in response to a detected atrial event towardthe end of the PVARP. Atrial detection inside the AFR window isclassified as refractory sensed and is not tracked. Tracking starts onlyafter both the AFR and the PVARP durations have expired.

Paced atrial events scheduled inside an AFR window are delayed (i.e.,inhibited) until the AFR window has expired, as is shown in FIG. 7.According to one approach, if there are fewer than 50 ms remainingbefore a ventricular pace, the atrial pace is inhibited for the cycle.The ventricular pace is not affected by AFR and will take place asscheduled. High-rate atrial sensing may continuously re-trigger the AFRwindow (i.e., extend the AFR window), effectively resulting in fallbackto an appropriate pacing mode (e.g., VDI(R)). FIG. 7 illustrates twosubsequent AFR windows initiated after the first AFR window due to thisre-triggering mechanism. Inhibiting atrial paces during atrial flutteror other high rate atrial activity advantageously provides for fastatrial sensing to be detected, thereby providing for faster satisfactionof atrial detection windows and, ultimately, faster detection decisions.

It has also been found that if the atrium is paced too soon after anatrial sense depolarization signal is sensed, it is theoreticallypossible that such premature delivery of an atrial pace signal caninduce an atrial arrhythmia. Inhibiting an atrial pacing function inthis case prevents induced atrial arrhythmias of this nature fromoccurring.

In accordance with one embodiment of the present invention, and withparticular reference to FIG. 3, the system 20 initiates atrialarrhythmia detection 200, such detection typically being an ongoingfunction of the system 20. The system 20 is programmed to implementseveral types of atrial arrhythmia detection algorithms as are known inthe art to detect 202 atrial arrhythmia, such as atrial flutter forexample. In response to detecting atrial arrhythmia, the system 20inhibits 204 atrial pacing to prevent competitive atrial pacing during aperiod of further evaluation.

The atrial arrhythmia is evaluated 206 while atrial pacing is inhibitedaccording to the detection algorithm employed by the system 20. If anatrial arrhythmia condition is confirmed 207 by the system 20, an atrialepisode is declared 208. Atrial therapy may be applied 210, ifappropriate, upon declaring the presence of a confirmed atrial episode.The capability to deliver atrial pacing signals to the atrium is enabled212 at an appropriate time, typically after the atrial arrhythmia (e.g.,atrial flutter) has ceased.

If an atrial arrhythmia condition is not confirmed 207 and the atrialarrhythmia has not ceased 209, the detection, inhibiting, and evaluationprocesses 202, 204, 206 are repeated. If an atrial arrhythmia conditionis not confirmed 207 and the atrial arrhythmia has ceased 209, thecapability to deliver atrial pacing signals to the atrium is enabled212.

FIG. 4 depicts various processes involving an atrial arrhythmiadetection methodology according to another embodiment of the presentinvention. According to this embodiment, and upon implementing 250 theatrial arrhythmia detection algorithm, atrial interval rates aredetected 251 and compared to a predetermined rate threshold. Forexample, the predetermined rate threshold may be indicative of an atrialrate associated with atrial flutter (e.g., 230 bpm). If the detectedatrial rate exceeds the predetermined rate threshold, atrial pacing isinhibited 252 so as to avoid competitive atrial pacing.

The system 20 detects the occurrence of atrial events 254, from whichatrial interval rates are developed 256 in a manner known in the art.Detecting atrial events 254 typically involves sensing of atrialP-waves. An atrial interval rate (i.e., an A-A wave time interval) iscomputed using the detected atrial P-waves. An average atrial intervalrate may also be computed.

An arrhythmia detection methodology of the present invention preferablyemploys a detection window when analyzing atrial rhythms. Uponinitiation 258 an atrial detection window procedure, an atrial detectionwindow is employed to classify 260 atrial intervals. The detectionparameters of the atrial window, such as window length and satisfactioncriteria, may be selected to provide for enhanced detection and responseto atrial arrhythmia episodes.

Each detected atrial interval rate processed in the atrial window iscompared to an atrial rate threshold as part of the atrial intervalclassification process 260. Based on this comparison, the atrialinterval rate is classified relative to one or more thresholds, such asrate thresholds. A detected atrial rate is classified as being a fastatrial interval, for example, if the atrial interval rate exceeds agiven atrial rate threshold. The atrial interval rate may also beclassified as slow based on another threshold.

The atrial interval rate samples buffered in the atrial window areevaluated to determined 262 if and when the atrial window is satisfied.The atrial window is satisfied when a predetermined number of the mostcurrent atrial intervals meet a preestablished satisfaction criterion.For example, the satisfaction criterion associated with the atrialwindow may be defined as n of the last m atrial intervals beingclassified as fast atrial intervals. The satisfaction criterion may, forexample, be expressed as a number (i.e., an integer), percentage orratio.

Once the atrial window becomes satisfied 264, and typically afterperforming one or more additional verification processes, an atrialepisode is declared 266. Atrial pacing is subsequently enabled 268(i.e., not withheld or inhibited) after the detected atrial arrhythmiahas ceased. If the atrial detection window is not satisfied 264 and theatrial arrhythmia has not ceased 265, the system 20 returns to theatrial detection process 254. If the atrial detection window is notsatisfied 264 and the atrial arrhythmia has ceased 265, the capabilityto deliver atrial pacing signals to the atrium is enabled 268.

As was discussed above, an A-A interval that ends with an atrial pace isdefined as a slow interval. If the atrial pacing function is notinhibited during atrial arrhythmia evaluation, atrial paces will likelybe interspersed with fast atrial senses. By inhibiting the atrial pacingfunction, the criteria for satisfying the atrial detection window occurssooner as compared to detection techniques that allow for atrial pacingduring atrial arrhythmia detection. Satisfying the atrial detectionwindow sooner provides for a more expeditious initiation of atrialtherapy delivery, when appropriate.

FIG. 5 illustrates several operations associated with an atrialarrhythmia detection methodology according to another embodiment of thepresent invention. It is understood that the detection andclassification operations depicted in FIG. 5 may be performed inconnection with a multiple rate zones implementation, but that a singlerate zone is assumed in the description of FIG. 5 for purposes ofclarity of explanation. Moreover, duration timers may be employed in theembodiment of FIG. 5, but are not included in the discussion of thisembodiment for purposes of clarity of explanation.

After initiating the atrial arrhythmia detection process 400, atrialinterval rates are detected 401 and compared to a predetermined ratethreshold. If the detected atrial rate exceeds the predetermined ratethreshold, atrial pacing is inhibited 402 under conditions discussedpreviously. Atrial events are detected, from which atrial intervals aredeveloped 404. Atrial interval rates are buffered and classified 406 inan atrial detection window of length L=X, where X typically rangesbetween 20 and 60 atrial interval rate samples.

The windowed atrial interval rates are compared 408 to a firstsatisfaction criterion. According to one configuration, for example, thefirst satisfaction criterion associated with the atrial window isdefined as 32 of the last 40 atrial intervals (80%) classified as fastatrial intervals. The comparison is made to determine if the atrialwindow is satisfied 410. If the atrial detection window is not satisfied410 and the atrial arrhythmia has not ceased 411, the system 20 returnsto the atrial detection process 404. If the atrial detection window isnot satisfied 410 and the atrial arrhythmia has ceased 411, thecapability to deliver atrial pacing signals to the atrium is enabled431.

FIG. 5B illustrates various processes associated with ending an atrialepisode. According the embodiment shown in FIG. 5B, and after an atrialepisode has been declared 412, atrial events are detected from whichatrial interval rates are developed 413. Atrial intervals are classified415 in the atrial window. If the atrial window remains satisfied 417, asmeasured against a maintenance satisfaction criterion (e.g., 24 of thelast 40 (60%) atrial intervals classified as fast), the system 20considers the same atrial episode to remain declared 419. The detectionand classification processes 413, 415, 417 are repeated.

If the atrial window becomes unsatisfied 417, such that the maintenancesatisfaction criterion is not met, an End of Episode (EoE) duration isinitiated 421. If the atrial window becomes satisfied 423 during the EoEduration, the EoE duration is terminated 425, and the system 20considers the same atrial episode to remain declared 419. The detectionand classification processes 413, 415, 417 are repeated.

If the atrial window remains unsatisfied 423 during and at theexpiration 427 of the EoE duration, the system 20 declares 429 theatrial episode to have ended. The system 20 returns to the detection,classification, and windowing processes depicted in FIG. 5A.

All or portions of an atrial arrhythmia detection methodology accordingto the present invention may be incorporated as part of new or existingarrhythmia detection schemes. For example, an exemplary dual atrial andventricular windowing methodology for detecting and verifying atrial andventricular arrhythmias is disclosed in U.S. Pat. No. 6,658,286 entitled“Atrial and Ventricular Tachyarrhythmia Detection System and Method,”which is hereby incorporated herein by reference. The atrial pacinginhibiting methodologies of the present invention may also beimplemented in the context of the atrial and ventricular detectionapproaches disclosed in commonly owned U.S. Pat. No. 5,978,707, which ishereby incorporated herein by reference. These or other known atrial orcombined atrial/ventricular arrhythmia detection methodologies may beemployed in combination with the present invention.

It will, of course, be understood that various modifications andadditions can be made to the preferred embodiments discussed hereinabovewithout departing from the scope of the present invention. Accordingly,the scope of the present invention should not be limited by theparticular embodiments described above, but should be defined only bythe claims set forth below and equivalents thereof.

1. A method implemented with an implantable medical device capable ofsensing and pacing at least an atrium of a heart, comprising: detecting,during an atrial arrhythmia, atrial events occurring within apost-ventricular atrial refractory period (PVARP); initiating adetection window in response to the detected atrial events, thedetection window having a length and a satisfaction criterion;inhibiting delivery of atrial pace signals for a duration of thedetection window; classifying, while inhibiting delivery of atrial pacesignals, atrial intervals in the detection window; and declaring anatrial episode in response to satisfying the detection window byevaluating the atrial intervals in the detection window with respect tothe satisfaction criterion.
 2. The method of claim 1, wherein inhibitingdelivery of the atrial pace signals comprises inhibiting delivery of theatrial pace signals in response to detecting atrial interval ratesindicative of atrial flutter.
 3. The method of claim 1, whereininhibiting delivery of the atrial pace signals comprises inhibitingdelivery of the atrial pace signals in response to detecting atrialinterval rates of at least about 130 bpm.
 4. The method of claim 1,wherein inhibiting delivery of the atrial pace signals comprisesinhibiting delivery of the atrial pace signals to cause an increase in arate of detection window satisfaction.
 5. The method of claim 1, furthercomprising enabling delivery of the atrial pace signals to the atriumafter ceasing of the atrial arrhythmia.
 6. The method of claim 1,wherein the detection window length ranges between 20 and 60 atrialinterval samples.
 7. The method of claim 1, wherein the satisfactioncriterion represents a predetermined number, percentage or ratio of theatrial intervals classified as fast atrial intervals relative to thedetection window length.
 8. The method of claim 1, wherein thesatisfaction criterion represents about 80 percent of the atrialintervals classified as fast atrial intervals.
 9. The method of claim 1,further comprising verifying that the declared atrial episode is asustained atrial episode in response to the detection window beingsatisfied by a second satisfaction criterion for subsequent atrialintervals.
 10. The method of claim 9, wherein each of the satisfactioncriterion and second satisfaction criterion represents a predeterminednumber, percentage or ratio of the atrial intervals classified as fastatrial intervals relative to the detection window length, and the secondsatisfaction criterion is less than the satisfaction criterion.
 11. Themethod of claim 10, wherein the satisfaction criterion represents about80 percent of the atrial intervals classified as fast atrial intervalsand the second satisfaction criterion represents about 60 percent of thesubsequent atrial intervals classified as fast atrial intervals.
 12. Abody implantable system, comprising: at least one lead comprising anatrial electrode for sensing and pacing an atrium of a heart; energydelivery circuitry coupled to the at least one lead; a detector, coupledto the at least one lead, configured to detect atrial events occurringwithin a post-ventricular atrial refractory period (PVARP) during anatrial arrhythmia; memory configured to define a detection window havinga length and a satisfaction criterion; and a control circuit coupled tothe energy delivery circuitry, detector and memory, the control circuitconfigured to initiate the detection window in response to the detectedatrial events, inhibit delivery of atrial pace signals for a duration ofthe detection window, classify, while inhibiting delivery of atrial pacesignals, atrial intervals in the detection window, and declare an atrialepisode in response to satisfying the detection window by evaluating theatrial intervals in the detection window with respect to thesatisfaction criterion.
 13. The system of claim 12, wherein the controlcircuit is configured to inhibit delivery of the atrial pace signals inresponse to detecting atrial interval rates indicative of atrialflutter.
 14. The system of claim 12, wherein the control circuit isconfigured to inhibit delivery of the atrial pace signals in response todetecting atrial interval rates of at least about 130 bpm.
 15. Thesystem of claim 12, wherein the control circuit is configured to inhibitdelivery of the atrial pace signals to cause an increase in a rate ofdetection window satisfaction.
 16. The system of claim 12, wherein thecontrol circuit is configured to enable delivery of the atrial pacesignals to the atrium after cessation of the atrial arrhythmia.
 17. Thesystem of claim 12, wherein the detection window length ranges between20 and 60 atrial interval samples.
 18. The system of claim 12, whereinthe satisfaction criterion represents a predetermined number, percentageor ratio of the atrial intervals classified as fast atrial intervalsrelative to the detection window length.
 19. The system of claim 12,wherein the satisfaction criterion represents about 80 percent of theatrial intervals classified as fast atrial intervals.
 20. The system ofclaim 12, wherein the control circuit is configured to verify that thedeclared atrial episode is a sustained atrial episode in response to thedetection window being satisfied by a second satisfaction criterion forsubsequent atrial intervals.
 21. The system of claim 20, wherein each ofthe satisfaction criterion and second satisfaction criterion representsa predetermined number, percentage or ratio of the atrial intervalsclassified as fast atrial intervals relative to the detection windowlength, and the second satisfaction criterion is less than thesatisfaction criterion.
 22. The system of claim 21, wherein thesatisfaction criterion represents about 80 percent of the atrialintervals classified as fast atrial intervals and the secondsatisfaction criterion represents about 60 percent of the subsequentatrial intervals classified as fast atrial intervals.
 23. A bodyimplantable system, comprising: means for detecting atrial eventsoccurring within a post-ventricular atrial refractory period (PVARP)during an atrial arrhythmia; means for initiating a detection window inresponse to the detected atrial events, the detection window having alength and a satisfaction criterion; means for inhibiting delivery ofatrial pace signals for a duration of the detection window; means forclassifying, while inhibiting delivery of atrial pace signals, atrialintervals in the detection window; and means for declaring an atrialepisode in response to satisfying the detection window by evaluating theatrial intervals in the detection window with respect to thesatisfaction criterion.
 24. The system of claim 23, comprising means forenabling delivery of the atrial pace signals to the atrium aftercessation of the atrial arrhythmia.
 25. The system of claim 23,comprising means for verifying that the declared atrial episode is asustained atrial episode in response to the detection window beingsatisfied by a second satisfaction criterion for subsequent atrialintervals.